SAN DIEGO — The Jets can whistle past the graveyard for as long as they choose.

They can talk about how “close” they are despite their 1-3 record and the current three-game losing streak they carry into Sunday’s game against the 3-1 Chargers at Qualcomm Stadium.

They can remind us that the season is only at the quarter pole and that they are merely one game out of first place in the AFC East.

Here’s the reality of the situation: This is it for the Jets.

Whether they choose to acknowledge it or not, the direction of their season will be precariously hanging in the balance when they play the Chargers on Sunday. Another loss — a fourth in a row — and the margin for error will become suffocating.

Three consecutive losses in the NFL is debilitating. Four-game losing streaks are difficult to come back from to make the playoffs. The Jets have done it twice — in 2002 when they fell to 1-4 after winning their opener and in 1986 when they lost their last five after a 10-1 start.

In the case of these Jets, if they leave San Diego on a four-game losing streak — with Peyton Manning and the Broncos visiting MetLife Stadium next Sunday followed by a Thursday night game in Foxborough, Mass., against the Patriots — there is a good chance that streak spirals to a five- or six-game skid.

Guard Willie Colon, one of the veteran leaders in the locker room, said he knows how the Jets have to respond Sunday, with so much stacked against them.

“I don’t think we have a choice. It’s time for us to wake up before it’s too late,” he said.

As this three-game losing streak has unfolded, public pressure has mounted significantly on coach Rex Ryan and quarterback Geno Smith, the second hand-picked franchise quarterback of his tenure (where have you gone, Mark Sanchez?).

Ryan’s future returned as a topic of conversation, and Smith, after cursing at a fan at the end of last Sunday’s loss, during the week showed some cracks in the mature, unaffected way he previously had behaved in the face of adversity.

Imagine the tenor should the Jets tumble to 1-6 and are faced with a final nine games of garbage time.

If it gets to that, then everything is on the table for the Jets — Ryan’s job, Smith’s career as a starter, general manager John Idzik’s questionable personnel decisions and drafts.

Everything.

This is admittedly a doomsayer view of things, but when you’re around the Jets for a long time, it becomes an inherent reaction.

“I think we’re close — a lot closer than people think,’’ Ryan said late in the week.

Jets fans have to hope so, because things are precariously close to team owner Woody Johnson blowing this whole thing up and starting over.

During a visit to the Jets’ locker room on Thursday, the day before they traveled to San Diego, the mood was upbeat. Players insisted they were not a desperate team.

Maybe they should be. The Jets need to treat this game as a matter of survival.

“We never envisioned being 1-3,’’ receiver David Nelson said. “Guys are encouraged about what we have been able to do at times, but discouraged at the won-loss record. We haven’t put whole games together, and this week we’re trying to do that.’’

The losing streak began when they blew a 21-3 lead to the Packers. Then, in losses to the Bears and Lions, it was the opposite — the Jets fell behind early and tried in vain to come back.

“What we can’t do is try to do too much too fast,’’ Nelson said. “Sometimes you see teams start to stress and try to make up three wins in one game, trying to make up three wins in one drive. We can’t put too much stress on ourselves.’’

Unfortunately, it might be too late.

“Right now, nobody believes in us but the people inside this organization,’’ safety Dawan Landry said. “It’s just us versus the world, really. We’re just a hungry team right now.’’

They are a hungry team and a desperate team.

“Playing desperate is the ability to play with a high sense of urgency where you don’t waste drives, you don’t waste plays, you take care of the minor details,” Colon said.

“We can’t sit back and accept another loss,’’ linebacker Quinton Coples said. “This is a point in the season where we have to win. This is definitely a must-win situation.’’